A silicon solar cell (mono-facial cell) by a conventional technique comprises a p-type silicon substrate, in which an n+ layer is formed by phosphorus diffusion and a grid-shape silver electrode in this order on the front side and with aluminum electrode over the entire back side, where these electrodes are formed by printing and firing process. More specifically, aluminum paste is printed and then fired at around 800° C., which diffuses the aluminum atoms into the silicon substrate to form the p+ layer on the back side. This p+ layer works as a back surface field (hereinafter referred to as BSF), which improves cell performance. At the same time, phosphorus gettering takes place while phosphorus is being diffused, and aluminum gettering takes place while the electrode is being fired, to improve life time of bulk silicon and cell performance. This conventional technique is disclosed in, for example, Patent document 1 below.
A bifacial cell with both sides serving as the photosensitive surfaces (photosensitive cell on both sides) is another technique, where a p-type silicon substrate is coated with an n+ layer formed by phosphorus diffusion to provide a n+p junction on the front side, and with a p+ BSF formed by boron diffusion and grid-shape electrode as a planar electrode on the back side. This type of bifacial cell has a low carrier life time, therefore the conversion efficiency when the back side is illuminated is around 60% or less to that when the front side is illuminated.
In a grid-shape electrode provided with finger and busbar electrodes in a solar cell by a conventional technique, the finger electrodes are arranged at the same interval of 120 to 140 μm until the electrode comes into contact with the busbar electrode.    (Patent Document 1): JP-A-10-144943 (Paragraphs 0026, 0027 and 0030).